Many of us use cordless tools when building or repairing our robots that
have NiCad or NiMH rechargeable batteries, but rarely do we know what the
battery’s actual mAh capacity is. (For some reason, manufacturers do not
include this information.) I was facing this problem. I had lots of power tool
batteries (over 20, mainly 12V and 18V) but they didn’t seem to hold a charge
very long or have much capacity. To determine the condition of these
batteries, I set up a relatively simple test system to measure a battery’s mAh
capacity using a PC, some load resistors, a serial port A/D, and some
software (VC#). My latest version uses a couple of relays and more A/D
channels to test two batteries simultaneously.